The long-range goal of the proposed research project is to obtain an understanding of the mechanisms of regulation in eukaryotic cells and to relate such information to the metabolism of cancer cells. The yeast Saccharomyces will be used as a model system. Cancer cells are characterized by an altered growth rate and morphology (both of which can be reversed by cyclic AMP in certain culture tissues) and an altered respiration. Therefore, more specifically, catabolite repression and its role in the regulation of enzyme synthesis and mitochondrial biogenesis will be studied by isolating mutations involving these aspects of yeast metabolism. In yeast, the biogenesis of mitochondria and the synthesis of the maltose, galactose and sucrose fermentation enzymes is repressed by glucose. Two methods are described by which one may isolate mutants of the catabolite repression system. The first method involves the use of glucosamine known to act as a gratuitous repressor in Saccharomyces inhibiting growth on glycerol. Mutants capable of growth on glycerol in the presence of glucosamine will be isolated. It is expected that a high proportion of these mutants will be insensitive to glucose in their ability to (1) elaborate a functional mitochondrion and/or to (2) synthesize the maltose, galactose and sucrose fermentative enzymes. The second method involves the selection of mutants which have, in a single mutagenic event, become incapable of growth on all of the following: maltose, sucrose and galactose. The three classes of mutants will be compared as to which glucose sensitive functions have been affected when the different selective procedures are used. Such comparisons should indicate the number of complementation groups involved in glucose repression and how many of these genes are common to both the repression of mitochondrial biogenesis and the repression of enzyme synthesis. In addition the levels of cyclic AMP in these mutants will be determined. This information should indicate whether cyclic AMP is of central importance in yeast, as it is in bacteria for catabolite repression.